So you probably know that we breathe out
CO2 and plants consume CO2
in the process of photosynthesis. In addition
there are many other sources of CO2 for
instance, when most things are burned, they
produce CO2. Volcanoes, hot springs,
and geysers also release CO2 into the
atmosphere. Deep under lakes and the world’s
oceans there is an abundance of CO2
dissolved in the water. In fact, there is 50 times
more carbon dioxide in the sea water than in the
atmosphere. All of these different sources of
CO2 are connected through the “Carbon
Cycle” which is important in making Earth
sustainable for life. One answer to your question
is that carbon dioxide comes from other sources of
carbon in the world.

A more cosmic question is where did the carbon
dioxide come in the first place? The answer to
this question is that Carbon and Oxygen are
produced deep within a massive star. These
elements are made from lighter elements in a
process called “nuclear fusion.” When a
star dies, its insides are thrown through space
and some of them will end up on a planet. This is
the original source of the carbon dioxide on
Earth.

Answer 2:

Carbon dioxide is generated from the oxidation of
carbon. So you have to have both oxygen and carbon
atoms and some energy to get the reaction started.
For example, you could have a spark that begins
the burning of coal (which contains mostly carbon)
in air which contains oxygen. This produces carbon
dioxide. Other sources of carbon dioxide include
animal respiration (we exhale carbon dioxide),
which is a result of the oxidation of
carbon-containing food that we eat for energy.
Burning wood or gas or other carbon-based fuels
also produces carbon dioxide.

Answer 3:

Carbon dioxide comes from many, many sources in
the world. Most commonly, though, it is the end
result of breaking big molecules into smaller
ones. Carbon dioxide is very energetically stable
(think: it does not burn) and it is so stable your
body cannot do anything with it. Plants can use it
because they use energy from the sun to build
other molecules with it, but this takes a lot of
energy. So, think of some processes that release
energy by breaking down bigger molecules into
smaller ones and energy. Combustion (burning fuel)
in a car engine breaks large hydrocarbons
(carbon-based molecules) into much smaller, more
stable carbon dioxide. This releases a lot of
energy, and also carbon dioxide. In the same way,
your body breaks down sugars and combines them
with oxygen you breathe to make carbon dioxide.
These are two main sources, but carbon dioxide
also occurs naturally.

Answer 4:

Carbon dioxide results when you combine carbon or
any carbon-containing compound with oxygen from
the atmosphere. You can also get it from
dissolving carbonate rocks in acid (and yes, water
is a very weak acid). You breathe in oxygen and
breathe out carbon dioxide, because the fuel that
your body runs on is carbon-containing molecules.
Burning almost anything will release carbon
dioxide (the exceptions are burning metals or
sulfur), since most things that burn contain
carbon.